2.1. General information and materials
All of the materials for synthesis were purchased from commercial suppliers and used without further purification. All of the solvents used were analytical reagent grade. Thin-layer chromatography (TLC) was conducted using silica gel 60 F254 plates (Merck KGaA). Column chromatography was carried out using silica gel powder 60-120 mesh (Ranbaxy). IR spectra were recorded on a VERTEX 70 FT-IR (Bruker Optics) IR spectrophotometer. 1H NMR spectra were recorded on a Bruker Avance 400 (400 MHz) spectrometer, using CDCl3 as solvent and tetramethylsilane (TMS) as an internal standard. Melting points were determined on an XD-4 digital micro melting point apparatus. HRMS spectra were recorded on a Q-TOF6510 spectrograph (Agilent). UV–vis spectra were recorded on a Perkin-Elmer Lambada-35 spectrophotometer. Fluorescence measurements were recorded on a Shimadzu RF-5301PC spectrofluorometer. All pH measurements were made with a pH-10C digital pH meter.
HEPES-buffer (5 mM, pH 7.4) were prepared in deionized water. The solution of metal ions were prepared from their perchlorate salts. All the measurements were performed at room temperature unless otherwise stated. Receptor 1 (6 mg, mM) and various metal ions were dissolved in ethanol (10 mL) as a stock solution (1 × 10-3 M) respectively. In experiments, the required concentration of the receptor 1 with HEPES- buffer (5 mM, pH 7.4) and the various metal ions solutions were diluted in the same way. The excitation and emission slit widths were kept constant (5 nm) throughout the optical studies. The fluorescence quantum yields (Φx) were determined by using 2-aminopyridine in 0.1 M sulfuric acid (Φstd) as standard and calculated by following reported procedure.
2.2. Synthesis receptor 1
1:1 molar ratio of 3-(1H-benzo[d]imidazol-2-yl)-2-chloroquinoline (BIQ)  0.5 g (1.8 mmol) and diethylene glycol 0.1 mL (0.9 mmol) with KOH 0.1 g (1.8 mmol) in 5 mL THF solvent were refluxed with stirred for 45 min. The solvent was removed under reduced pressure and the crude was transferred to a beaker containing crushed ice and neutralized using dil.HCl solution. The formed white precipitate was filtered, dried and adsorbed for the silica (120-200 mesh) column chromatography. The pure product was isolated...